Speech understanding in noisy environments is a significant problem for the hearing-impaired. Hearing impairment is usually accompanied by a reduced time resolution of the sensorial system in addition to a gain loss. These characteristics further reduce the ability of the hearing-impaired to filter the target source from the background noise and particularly to understand speech in noisy environments.
Some newer hearing aids offer a directional hearing mode to improve speech intelligibility in noisy environments. This mode makes use of an array of microphones and applies beamforming technology to combine multiple microphone inputs into a single, directional audio output channel. The output channel has spatial characteristics that increase the contribution of acoustic waves arriving from the target direction relative to those of the acoustic waves from other directions. Widrow and Luo survey the theory and practice of directional hearing aids in “Microphone arrays for hearing aids: An overview,” Speech Communication 39 (2003), pages 139-146, which is incorporated herein by reference.
PCT International Publication WO 2017/158507, whose disclosure is incorporated herein by reference, describes hearing aid apparatus, including a case, which is configured to be physically fixed to a mobile telephone. An array of microphones are spaced apart within the case and are configured to produce electrical signals in response to acoustical inputs to the microphones. An interface is fixed within the case, along with processing circuitry, which is coupled to receive and process the electrical signals from the microphones so as to generate a combined signal for output via the interface. In some embodiments, the processing circuitry mixes the electrical signals in accordance with a directional response that is dependent on the angular orientation of the case, and thus generates audio output to an earphone (or pair of earphones) worn by the user.